Although grammatical deficits frequently characterize specific language impairment (SLI), very little is known about the complex syntax development of children with SLI.From theoretical as well as clinical perspectives, empirical exploration of complex grammar acquistion is needed to better understand the entirety of grammatical deficits associated with SLI. Thus, the PI has embarked upon a program of empirical studies of complex syntax in children with SLI in order to assess various theory-driven hypotheses regarding how limitations in complex syntax relate to other well-established grammatical deficits in children withSLI. In general, the proposed study represents an initial step in describing and quantifying the complex syntax acquisition of children with SLI. The specific aims are two-fold: a) To establish methodology for investigation of complex syntax production in young children, particularly variables that are sensitive to developmental change and that differentiate typical language children from children with SLI;and (b) To describe the acquisition of complex syntax production in children with SLI across an 18-month period beginning at 5 years of age as compared to age-matched typical children and language-matched, but chronologically younger, typical children. It is hypothesized that children with SLI will produce complex syntax less frequently than age- or language- matched peers. It is further hypothesized that the grammatical structure of complex syntax will prove more challenging for the children with SLI.Thus, inclusion of formal grammatical elements associated with the complementizer system (e.g., relative that) may be deficient for children with SLI,relative to their age- and language-matched peers. Such findings may be taken to suggest that these deficits contribute to the difficulties SLI children have establishing reasonably typical grammatical usage. Findings should have appreciable implications for theoretical accounts of the nature of grammatical deficits in children with SLI and should contribute to the database needed to most adequately assess and treat these children.